Antioxidants constitute one popular class of supplements touted to have anti-aging powers. Such chemicals occur naturally in the body and in fruits and vegetables and are believed to neutralize free radicals. Proponents claim that if taken in sufficient quantities, antioxidant supplements will sop up the radicals and slow down or stop the processes responsible for aging. But eliminating all free radicals would kill us, because they perform certain necessary intermediary steps in biochemical reactions. Further, although epidemiological studies have demonstrated that the antioxidant vitamins E and C contained within the foods we eat may reduce the risk of cancer, macular degeneration and other disorders, no one has established that vitamin supplements containing antioxidants limit oxidative damage in the body or influence aging.
Like antioxidants, another fashionable anti-aging intervention, hormone replacement, has a plausible rationale. This strategy was first popularized early in the 20th century, when older men occasionally submitted to the grafting of testicles from goats or monkeys or received injections of macerated testicles. Today pure forms of hormones can be administered. The replacement strategy seems logical in principle because the blood levels of most hormones—among them melatonin, growth hormone, testosterone and dehydroepiandrosterone (DHEA)—commonly decrease with age. Also, experiments on older men have demonstrated that some physical and physiological attributes that show declines over time, notably muscle mass and skin elasticity, respond favorably in the short term to growth hormone replacement.
On the other hand, hormones can cause worrisome side effects. In mice, for instance, delivery of melatonin increases the risk of tumor development, and the over-production of growth hormone leads to kidney problems, premature heart and lung failure, and an increased probability of early death. Human adults given growth hormone have suffered from acromegaly (excess bone growth) and carpal tunnel syndrome. Estrogen replace-
ment therapy may offer health benefits to some postmenopausal women; however, this form of therapy has recently been challenged and has risks of its own, such as breast cancer and blood clots. In short, hormone replacement therapy has a place in the treatment of specific age-associated disorders, but evidence that it affects the rate of aging is lacking.
Some people might wonder whether following today’s public health recommendations for diet and exercise can serve as a more natural Fountain of Youth. Good nutrition and regular exercise do reduce the risk of various diseases and, in that way, may extend the duration of life for many people—thereby serving as the best current prescription for a long and healthy life. As is true of other interventions, though, no one has shown that diet or exercise, or both, directly influences aging.
What Science Says We find it ironic that a phony anti-aging industry is proliferating today, because serious efforts to understand aging have advanced greatly in recent years. Biologists who work with yeast, roundworms, fruit flies and mice have extended life by manipulating the genes of those species. These genetic alterations did not affect what is believed to be an important hallmark of aging in a population (an exponential increase in the risk of dying with time after puberty), which means that the longevity extensions in those experiments cannot safely be interpreted as resulting from an intervention in the aging process. Nevertheless, further study of those genes could offer clues to the influences on longevity and to approaches that might postpone infirmity and age-related disorders.
Another avenue of research may also lead to true aging interventions. Investigators have known for decades that caloric restriction extends life and the duration of good health in all species in which it has been studied, as long as the diet includes enough nutrition for routine maintenance of the body. These findings suggest that caloric restriction might have similar effects in humans. Given that few people would ever reduce their food intake enough to lengthen their lives, biologists are now trying to discover the mechanism that underlies the benefits of caloric restriction and to find agents that might mimic those helpful effects in people without forcing them to go hungry.